Polymeric films are widely used in packaging applications for various food and non-food items. When unmodified, such films often lack sufficient moisture and gas barrier properties needed for many packaging applications. For example, biaxially-oriented, polypropylene films are particularly preferred in the manufacture of packaging films due to their low cost and good mechanical properties. Although such films may offer good moisture barrier properties, they lack suitable gas barrier properties for many packaging applications.
Metallic films, such as aluminum foil, are well known in the art for packaging applications. Such metallic films may have both desirable moisture and gas barrier properties, but are high cost. Also, metallic films lack mechanical properties suitable for many packaging applications.
To improve gas and moisture barrier properties, multi-layer films have been developed that offer the advantages of both polymeric films and metallic films. Such multi-layer films may typically comprise a polymeric core layer in combination with one or more other polymeric layers or metallized layers. For example, metallized, high barrier films may typically have an oriented polypropylene film core layer, a metallized layer and a sealant layer. Although these high barrier films may provide good moisture and gas barrier properties and good optical properties, such films may be difficult to manufacture and their moisture barrier properties may decline after end-use packaging operations.
Multi-layer, metallized films comprised of one or more layers containing ethylene vinyl alcohol (“EVOH”) polymers may have good gas barrier properties, but exhibit weak moisture barrier properties. To improve moisture barrier properties, EVOH-containing films have been co-extruded with high-density polyethylene. Such co-extruded films may exhibit superior gas barrier properties, very good moisture barrier properties, but may have significant manufacturing issues, such as die lip build up and unstable thin layer co-extrusion quality. Moreover, such co-extruded films may not exhibit an optical appearance that is comparable to the mirror-like appearance of aluminum foil or metallized, polyethylene terephthalate (METPET) film.
Metallized, lactic acid polymer films (MET PLA) have a core layer comprised of a homopolymer of lactic acid, or a copolymer of lactic acid and another polymer, as disclosed in U.S. Pat. No. 5,556,711, the specification of which is incorporated herein by reference. MET PLA films may have desirable gas barrier properties and desirable mechanical properties. However, such MET PLA films are not suitable in many packaging applications because of high moisture permeability.
Hence, there is a need for a multi-layer film that has desirable moisture and gas barrier properties and displays a mirror-like appearance. Such a film should retain its desirable barrier properties after end-use packaging operations and be competitive with prior art films. The present invention meets this and other needs.